One of the operative treatments used to treat cataract is a method of removing a natural crystalline lens from an eye of a patient and then injecting an intraocular lens (IOL) in place of the natural crystalline lens.
The majority of first generation IOLs were manufactured from rigid PMMA and were implanted into the eye using forceps through large (5-6 mm) incisions. The large incision size increased the risk of infection and could lead to induced changes in the shape of the cornea and also potentially cause astigmatism of the eye after the operation. To prevent such disadvantages, a next generation of foldable IOLs was developed that could be introduced into the eye through a reduced incision size (2-4 mm) using an injector.
IOLs typically comprise a lens portion and a pair of resilient haptics extending outwardly from opposite sides of the periphery of the lens portion. The haptics aid in locating the IOL in a correct position in the eye and in maintaining the IOL in that correct position.
To inject the IOL, the following steps are usually performed: first making an incision in the eye; fragmenting and aspirating a clouded natural crystalline lens through the incision; and then injecting the IOL into the eye through the incision to implant it in place of the natural crystalline lens.
A first generation of injectors typically consisted of reusable titanium bodies fitted with disposable plastic cartridges, those cartridges being loaded with a foldable IOL at the point of use.
With reference to FIGS. 1a and 1b, the next generation of injectors 10 were plastic, disposable, single-use injectors. These often had cartridges 20 that were integral with the injector bodies 12, the IOL 50 being inserted at the point of use as in the previous injectors mentioned above. It is also known for the cartridge 20 to be a separate element, removably fitted into a loading bay of the injector 10. The foldable IOL 50 in the cartridge 20 is positioned so as to be aligned with a bore 14 in the injector 10 containing a plunger 16. A relatively narrow end portion 16′ of the plunger engages the IOL 50 to urge the IOL toward the tip 18 of the injector. In some cartridges 20, the IOL 50 is held within the injector 10 and engaged by the plunger 16 in an unfolded state, in which case the tip 18 of the injector 10 will be tapered so as to fold the IOL into a smaller shape as it is pushed toward and through the tip 18 by the plunger 16. In other cartridges 20, the IOL 50 is folded just prior to insertion by manipulation of the cartridge 20 and is engaged by the plunger 16 in a folded condition, as described below. The folded IOL 50 is pushed out of the tip 18 of the injector 10 inserted in the eye through the incision and is spread (unfolded) and placed in the eye.
It is essential for IOLs 50 to be stored unstressed so as not to become permanently deformed over time. Accordingly, IOLs 50 are not held in a folded condition over a long period of time (i.e. in storage).
More recently, disposable, single-use injectors 10 have come preloaded with an IOL 50. Preloaded injectors designed for delivery of hydrophobic IOLs usually incorporate lens storage within the main injector body. Due to its simplicity, this is a more preferable option for a preloaded injector and is possible because hydrophobic IOLs can be stored in a non-hydrated or ‘dry’ state. Examples of known preloaded systems include four fully preloaded injectors: Isert Acrylat, hydrophobic aspheric; Acrysert Acrylat, hydrophobic aspheric; NX-1 Nex-load Acrylat, hydrophobic aspheric; and KS3-Ai Silicone aspheric (respectively manufactured by Hoya, Alcon, Domilens and STAAR-Domilens).
In contrast to hydrophobic IOLs, hydrophilic IOLs must be stored hydrated, normally completely submerged in a saline solution. As a consequence, semi-preloaded injectors for hydrophilic IOLs, requiring insertion of a cartridge into the injector by the end user, are used for hydrophilic IOLs. The IOL is held within a cartridge submerged in saline during storage, then removed and attached to the main body of an injector (dry) immediately prior to use, much as described above in connection with the early titanium injectors 10. Examples of known semi-preloaded injectors include: Polysert PPS Acrylat, hydrophobic aspheric; XL Stabi Sky Acrylat, Hydrophilic, aspheric; and Slimflex m1.2.3, Acrylat hydrophilic, aspheric (respectively manufactured by Polytech, Zeiss and Technoko).
The clinical argument for preloaded lenses is convincing. Manual loading of IOLs into injectors is usually carried out by the end user (e.g. a nurse or a surgeon), often in low light and under the stress of operating theatre conditions. Since manual insertion of the lens into the cartridge is not necessary with preloaded injectors, there is no additional risk of contamination, no mechanical damage because of contact with the lens by instruments, no 180° upside-down confusion, and no loss of the IOL on the operating table. Injection of the IOL is standardized. The injector systems themselves are all disposable materials; there is absolutely no more need for complicated preparation of the instruments for re-use.
As mentioned above, with some known cartridges 20, the IOL 50 may be held in an unfolded state within the injector 10. Accordingly, when the cartridge 20 is inserted into the injector 10, the IOL remains unfolded. It is only once the IOL is engaged and urged out of the tip 18 of the injector by the plunger 16 that the IOL becomes folded for injection through the incision in the eye.
In some known cartridges, the cartridge is manipulated prior to insertion into the injector in order to fold the IOL within. For example, the currently most common IOL injector cartridge format includes a pair of hinged flaps that, in a first configuration, define a chamber that holds the IOL in an unfolded state. When the flaps are hinged together, the chamber becomes reduced in size, thus folding the IOL within. This is also the case with integral cartridges; the IOL is inserted into a loading bay of the injector (defined within the integral cartridge) at the point of use in an unfolded state and the flaps of the cartridge are then closed to fold the IOL.